A mold type semiconductor device (i.e., a semiconductor package) includes a semiconductor chip molded with resin. The semiconductor chip includes a semiconductor part such as an insulated gate bipolar transistor (i.e., IGBT). Specifically, the semiconductor package is disclosed in Japanese Patent Application Publication No. 2003-110064.
As shown in FIG. 15, the semiconductor package 36 includes a semiconductor chip 37 having an IGBT disposed on a semiconductor substrate, a lower side heat sink 38, an upper side heat sink 39 and an inner heat sink 40. The lower side heat sink 38 connects to a collector electrode of the IGBT, and the upper side heat sink 39 connects to an emitter electrode of the IGBT. The inner heat sink 40 is disposed on the top of the semiconductor chip 37. Each part is electrically connected together with a solder layer 41. A gate electrode of the semiconductor chip 37 is connected to a lead frame 42 with a gate wire 43. One side of the lower side heat sink 38 is exposed from a resin mold 44. Further, one side of the upper side heat sink 39 is also exposed from the resin mold 44, and a part of the lead frame 42 is exposed from the resin mold 44. Thus, the resin mold 44 seals the parts so that the semiconductor package 36 is provided.
The semiconductor package 36 is formed such that melted resin material pours into a mold after all parts is mounted in the mold. Then, the melted resin material is cooled and solidified so that the semiconductor package 36 is provided. At this time, the melted resin is heated up to about 180° C. Therefore, each part in the semiconductor package 36 is heated by the melted resin material. Although a stress is generated in accordance with a difference of linear expansion coefficients of the parts in the semiconductor package 36, the stress is absorbed by the solder layer 41, which connects between the parts.
However, in a case where the stress is comparatively large, the solder layer 41 cannot absorb the stress enough so that the stress is applied to the semiconductor substrate. Here, the emitter electrode of the IGBT and the IGBT itself are formed in the substrate. Therefore, when the stress is applied to the emitter electrode and the substrate, an aluminum layer composing the emitter electrode may be cracked so that the emitter electrode is removed from the substrate or the emitter electrode is damaged. Thus, the IGBT does not work precisely, or the crack prevents heat conduction so that the heat is accumulated in the IGBT. Therefore, the accumulated heat in the IGBT may damage the IGBT.
Further, when the semiconductor package 36 is mounted on equipment for operating the semiconductor chip 37, the semiconductor chip 37 generates heat so that the semiconductor package 36 is heated up to a comparatively high-temperature. Further, the semiconductor package 36 is cooled by an atmospheric temperature in usage environment. The semiconductor package 36 is applied with thermal stress under thermal cycle, so that the emitter electrode and/or the IGBT may be damaged.
Furthermore, in a case where the solder layer 41 is made of lead free solder or the like, which is comparatively hard, the above crack is generated much more.